The U.S. economic market potential for distributed generation is significant. This market, however, remains mostly untapped in the commercial and small industrial buildings that are well suited for microturbines.
Gas turbines have many advantages, including high power density, light weight, clean emissions, fuel flexibility, low vibration, low maintenance, high reliability, and excellent durability. These power generation systems are frequently used for aviation, utility power, and remote oil and gas applications.
This project developed a 370 kW gas-fueled microturbine that would provide entry into additional markets because of its increased energy efficiency and reduced capital cost, which is estimated to be approximately $600 per kW. The microturbine technology maximizes usable exhaust energy and achieves ultra-low emissions levels.
The initial target for the C370 microturbine is the distributed generation market using existing fuel infrastructure, including fossil fuels, such as natural gas and diesel, as well as renewable fuels, such as landfill gas, digester gas, and syngas.
The objective of this project was to demonstrate a microturbine based distributed generation system with increased efficiency, reduced emissions, and improved customer value. The highest risk technical challenges were addressed early in the project and many components from current Capstone products were used to accelerate development.
The project used a modified Capstone C200 compressor and turbine assembly to act as the low-pressure section of a two-shaft turbine system. This resulted in an electrical output of 250 kW. A new high-temperature, high-pressure compressor and turbine acted as the second assembly. After an intercooler and the high-pressure assembly were added, the electrical output increased to 370 kW.
Capstone Turbine Corporation led this project. Oak Ridge National Laboratory (ORNL) and the NASA Glenn Research Center supported Capstone on specific project objectives. ORNL assisted with the high-pressure recuperator and high-temperature radial turbine materials. NASA Glenn evaluated a larger air bearing design for the high-speed generator.
The first phase of the project was to design and demonstrate the elements of the C370 CHP system that represented the greatest challenges of technical development. Capstone designed and integrated a low-pressure compressor and turbine system using a modified version of the C200; high-pressure, high-temperature compressor and turbine system; a combustion system; an intercooler; and high-pressure recuperator to create a two-shaft C370 engine.
Capstone then integrated heat recovery technology to complete the C370 CHP system. Integrated prototype system performance was estimated by utilizing a design cycle model.
The C200 was developed in part with support from the U.S. Department of Energy’s Advanced Microturbine Systems program in the early 2000s. The 200 kW microturbine has a net electrical efficiency of 33%; this project proved that achieving 42% net electrical efficiency and 85% total system efficiency in a CHP application for the C370 is feasible. Such high efficiency combined with emissions levels that are below California Air Resources Board (CARB) requirements and competitive capital cost of $600 per kW is expected to make the C370 an attractive product in the marketplace.
Before entering the market, however, some remaining technical challenges—including durability of the bi-metallic turbine wheel and control system architecture for the high-speed system—need to be overcome. Once the product is ready for the market, Capstone will use its current distributor and original equipment manufacturer (OEM) business model to directly market the C370 microturbine CHP system.